''Pennella exocoeti'' is a large

ectoparasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

, a specialist parasite of

flying fish The Exocoetidae are a family of marine fish in the order Beloniformes class Actinopterygii, known colloquially as flying fish or flying cod. About 64 species are grouped in seven to nine genera. While they cannot fly in the same way a bird do ...

. The adult female copepod clings to the fish's gills or skin and feeds on its body fluids.

Taxonomy

''Pennella exocoeti'' was first described by the Danish zoologist Hans Severin Holten in 1802 from a specimen probably found on the

mirrorwing flyingfish The mirrorwing flyingfish (''Hirundichthys speculiger'') is a flying fish of the family Exocoetidae. It was first described by the French zoologist, Achille Valenciennes in a 22-volume work titled ''Histoire naturelle des poissons'' (''Natural Hi ...

(''Hirundichthys speculiger''). He called it a "gill worm" and recognised that it had close affinities with '' Chondracanthus merluccii'', another "gill worm" found on a member of the cod family

Gadidae The Gadidae are a family of marine fish, included in the order Gadiformes, known as the cods, codfishes, or true cods. It contains several commercially important fishes, including the cod, haddock, whiting, and pollock. Most gadid species are ...

, but he did not realise they were both copepods. Another species was described by the French naturalist

Charles Alexandre Lesueur Charles Alexandre Lesueur (1 January 1778 in Le Havre – 12 December 1846 in Le Havre) was a French Natural history, naturalist, artist, and explorer. He was a prolific natural-history collector, gathering many type specimens in Australia, ...

as ''Pennella blainvilli'' from the tropical two-wing flyingfish (''

Exocoetus volitans ''Exocoetus volitans'', commonly known as the tropical two-wing flyingfish or blue flyingfish, is a species of ray-finned fish native to tropical and subtropical seas. It can glide above the surface of the sea to escape predators. Description T ...

''), but that has since been determined to be a synonym of ''P. exocoeti''.

Description

This is a large copepod that may grow to a length of . The mature female found attached to its host bears little resemblance to a free-living copepod. The mouthparts are adapted for piercing the host's cuticle and sucking fluids, the second antennae are modified with hooked claws for gripping the host, and the other appendages are vestigial. The body gradually widens towards the posterior and has transverse bands of dark colour. The body terminates with an egg sac and a pair of very long

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

e (bristles).

Ecology

The adult female copepod is parasitic while the adult male is free-living. The head and neck of the female burrow into the host fish and large, hard cysts are formed in the host's organs. The attachment is made by hooking to the fish with the prehensile second antennae, the remaining parts of the copepod's body hanging free. This copepod is in its turn often parasitised by a

goose barnacle Goose barnacles, also called stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Ped ...

, ''

Conchoderma virgatum ''Conchoderma virgatum'' is a species of goose barnacle in the family Lepadidae. It is a pelagic species found in open water in most of the world's oceans attached to drifting objects or marine organisms. Description ''Conchoderma virgatum'' has ...

''.

References

{{Taxonbar, from=Q14073474 Siphonostomatoida Parasitic crustaceans Crustaceans described in 1802